MARS BOUNDARY-LAYER MODELING - DIURNAL MOISTURE CYCLE AND SOIL PROPERTIES AT THE VIKING-LANDER-1 SITE

A dusty and moist martian atmospheric boundary layer model was augmented with a soil temperature diffusion scheme, simple soil hydrology, and interactive icecloud physics. It was applied to the summertime conditions at the Viking Lander 1 site (48 degrees W, 22.5 degrees N). A good simulation of the observed 1.6-m diurnal VL-1 temperature cycle was obtained when the soil properties were adjusted to that of a dryish at least 7-cm-thick sandlike topsoil layer with water availability of 0.05%, thermal conductivity of 0.18 W m(-1) K-1, and volumetric heat capacity of 0.8 x 10(6) J m(-3) K-1. The cold nighttime temperatures lead to saturation of water vapor and surface fog formation in the model. The radiation fog extended to 60-80-m altitudes during the night, but remained thin, with maximum ice content of 0.05 g m(-3) at 1.6 m height and vertical ice-waterpath of 0.43 precipitable (pr) mu m by 07 LT. The fog dispersed within two hours after sunrise. The column water vapor amount stayed at about 16 pr mu m (close to the Viking MAWD observations), being well mixed in the lowest 3 km with mixing ratios of about 0.18 g/kg, except near the surface where the ground sublimation/frosting and the condensation/sublimation into/from fog created a clear diurnal cycle. The 1.6-m relative humidities hit 100% at night (22-07 LT) but dropped below 1% in the afternoon. (C) 1995 Academic Press, Inc.